http://prntscr.com/mevuf1
I just received this coupon, and when I try to use, it says: "No results were returned for that query".
According to steamdb, this is the app: https://steamdb.info/sub/320322/info/

Hello there, fellow soilders, its been a while, but its here, Metal Slug (the very first one) is now on steam, and what's better than to do a simple, yet effective achievement guide, which, if with enough skill and determination, you can get all of the ach...